1. Field of the Invention
The present invention relates to a gas flow monitoring system for monitoring flow rate accuracy of a flow control device (a mass flow controller and others) used in a gas supply system for a process gas or the like in a semiconductor manufacturing device.
2. Related Art
In coating devices, dry etching devices, and others in a semiconductor manufacturing process, for example, a special gas such as silane, a corrosive gas such as chlorine gas, a flammable gas such as hydrogen gas and phosphine are used. Their gas flow rates have a direct influence on the quality of products to be manufactured and thus have to be strictly controlled. In particular, in association with recent laminating and miniaturizing of semiconductor substrates, improved reliability in a process gas supply system are demanded more than before.
Therefore, for example, Patent Document 1 discloses a flow control technique for supplying gas in a semiconductor manufacturing process.
In this technique in Patent Document 1, a pressure gauge and a final cutoff valve are provided downstream of a mass flow controller (MFC) to accurately calculate a gas flow rate to be discharged to a process chamber. After the final cutoff valve is closed, a pressure rise measured by the pressure gauge is sampled at predetermined time intervals and then a pressure inclination angle is calculated in a high correlation coefficient range from the sampled date to calculate a flow rate of the MFC. Patent Document 1 also discloses that a cutoff valve and a pressure gauge are provided upstream of the MFC. In this case, after the cutoff valve is closed, a pressure drop measured by the pressure gauge is sampled at predetermined time intervals and then a pressure inclination angle is calculated in a high correlation coefficient range from the sampled date.